There is known a rotation drive apparatus which is provided in a construction machine such as an excavator and includes an electric motor (rotation motor) for rotating an upper rotary body of the construction machine. Furthermore, there is also known a type that includes a parking brake which operates, when the upper rotary body is in a rotation stopped state, to hold the upper rotary body in the stopped state (see Patent Literature 1).
Such construction machines include one having a function to activate the parking brake to stop a rotation when an operator or the like applies an emergency stop operation to a switch or the like. However, in this type of construction machine, the parking brake is activated to stop the rotation also when the emergency stop operation is performed in spite of no rotation failure condition, for example, when an operation by an operator based on an erroneous failure judgement, or owing to misrecognition or accidental contact, or an experimental operation by an operator or a worker other than the operator, is performed. This uselessly increases the activation frequency of the parking brake. Furthermore, the parking brake, which is originally designed with an assumption that it operates under a rotation stopped condition, gets greatly damaged when activated for stopping during a rotation. The above-described wasteful rotation stopping action, thus, accelerates damage to the parking brake; this may prevent the parking brake from fulfilling its original stop holding function or reduce the lifetime of the parking brake.